BeanDefinition

浅浅的花香味﹌ 2024-03-16 17:15 45阅读 0赞

BeanDefinition 是 Spring 中的一个核心概念，它用于描述一个 Bean 实例的属性和行为，并提供了创建和管理 Bean 实例的基础信息。

在 Spring 中，IOC 容器是负责管理 Bean 实例的创建、初始化和依赖注入等过程的核心组件。BeanDefinition 描述了一个 Bean 实例的基本信息，包括 Bean 的类型、属性、构造函数参数、初始化方法、销毁方法等。IOC 容器根据这些信息来创建和管理 Bean 实例，使得开发者无需手动创建和管理 Bean 实例，从而实现了控制反转。

在 Spring 中，AOP（面向切面编程）框架是实现横切关注点的重要方式之一。在 AOP 中，需要对目标对象进行代理，并在代理对象中增加横切逻辑。BeanDefinition 是实现 AOP 的基础，它定义了需要被代理的 Bean 实例以及代理所需的相关信息，从而实现了 AOP 功能。

在 Spring 中，很多功能都是通过扩展机制实现的。例如，Spring 提供了一系列的 BeanPostProcessor 和 BeanFactoryPostProcessor 接口，用于在 Bean 实例化和依赖注入过程中进行扩展。BeanDefinition 是实现扩展机制的基础，它提供了对 Bean 实例化和依赖注入过程的描述，从而使得开发者可以通过实现相应的接口来扩展 Spring 的功能。

*  BeanDefinition

/**
 * A BeanDefinition describes a bean instance, which has property values,
 * constructor argument values, and further information supplied by
 * concrete implementations.
 *
 * This is just a minimal interface: The main intention is to allow a
 * {@link BeanFactoryPostProcessor} to introspect and modify property values
 * and other bean metadata.
 *
 
 public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {}

*  setParentName(String parentName) 和 getParentName()：设置和获取父 Bean 的名称。

/**
    	 * Set the name of the parent definition of this bean definition, if any.
    	 */
    	void setParentName(@Nullable String parentName);
    
    	/**
    	 * Return the name of the parent definition of this bean definition, if any.
    	 */
    	@Nullable
    	String getParentName();

*  setBeanClassName(String beanClassName) 和 getBeanClassName()：设置和获取 Bean 的完全限定类名。

void setBeanClassName(@Nullable String beanClassName);
 
 /**
 	 * Return the current bean class name of this bean definition.
 	 * Note that this does not have to be the actual class name used at runtime, in
 	 * case of a child definition overriding/inheriting the class name from its parent.
 	 * Also, this may just be the class that a factory method is called on, or it may
 	 * even be empty in case of a factory bean reference that a method is called on.
 	 * Hence, do not consider this to be the definitive bean type at runtime but
 	 * rather only use it for parsing purposes at the individual bean definition level.
 	 * @see #getParentName()
 	 * @see #getFactoryBeanName()
 	 * @see #getFactoryMethodName()
 	 */
 	@Nullable
 	String getBeanClassName();

*  setScope(String scope) 和 getScope()：设置和获取 Bean 的作用域。

/**
    	 * Override the target scope of this bean, specifying a new scope name.
    	 * @see #SCOPE_SINGLETON
    	 * @see #SCOPE_PROTOTYPE
    	 */
    	void setScope(@Nullable String scope);
    
    	/**
    	 * Return the name of the current target scope for this bean,
    	 * or {@code null} if not known yet.
    	 */
    	@Nullable
    	String getScope();

*  setLazyInit(boolean lazyInit) 和 isLazyInit()：设置和获取 Bean 是否懒加载。

/**
 	 * Set whether this bean should be lazily initialized.
 	 * If {@code false}, the bean will get instantiated on startup by bean
 	 * factories that perform eager initialization of singletons.
 	 */
 	void setLazyInit(boolean lazyInit);
 
 	/**
 	 * Return whether this bean should be lazily initialized, i.e. not
 	 * eagerly instantiated on startup. Only applicable to a singleton bean.
 	 */
 	boolean isLazyInit();

*  setDependsOn(String... dependsOn) 和 getDependsOn()：设置和获取 Bean 的依赖关系，即在实例化该 Bean 之前需要先实例化的其他 Bean 名称。

/**
    	 * Set the names of the beans that this bean depends on being initialized.
    	 * The bean factory will guarantee that these beans get initialized first.
    	 */
    	void setDependsOn(@Nullable String... dependsOn);
    
    	/**
    	 * Return the bean names that this bean depends on.
    	 */
    	@Nullable
    	String[] getDependsOn();

*  setAutowireCandidate(boolean autowireCandidate) 和 isAutowireCandidate()：设置和获取 Bean 是否可以被自动装配。

/**
 	 * Set whether this bean is a candidate for getting autowired into some other bean.
 	 * Note that this flag is designed to only affect type-based autowiring.
 	 * It does not affect explicit references by name, which will get resolved even
 	 * if the specified bean is not marked as an autowire candidate. As a consequence,
 	 * autowiring by name will nevertheless inject a bean if the name matches.
 	 */
 	void setAutowireCandidate(boolean autowireCandidate);
 
 	/**
 	 * Return whether this bean is a candidate for getting autowired into some other bean.
 	 */
 	boolean isAutowireCandidate();

*  setPrimary(boolean primary) 和 isPrimary()：设置和获取 Bean 是否为首选 Bean。

/**
 	 * Set whether this bean is a primary autowire candidate.
 	 * If this value is {@code true} for exactly one bean among multiple
 	 * matching candidates, it will serve as a tie-breaker.
 	 */
 	void setPrimary(boolean primary);
 
 	/**
 	 * Return whether this bean is a primary autowire candidate.
 	 */
 	boolean isPrimary();

*  setFactoryBeanName(String factoryBeanName) 和 getFactoryBeanName()：设置和获取 FactoryBean 的名称。

/**
    	 * Specify the factory bean to use, if any.
    	 * This the name of the bean to call the specified factory method on.
    	 * @see #setFactoryMethodName
    	 */
    	void setFactoryBeanName(@Nullable String factoryBeanName);
    
    	/**
    	 * Return the factory bean name, if any.
    	 */
    	@Nullable
    	String getFactoryBeanName();

*  setFactoryMethodName(String factoryMethodName) 和 getFactoryMethodName()：设置和获取 FactoryBean 的工厂方法名称。

/**
    	 * Specify a factory method, if any. This method will be invoked with
    	 * constructor arguments, or with no arguments if none are specified.
    	 * The method will be invoked on the specified factory bean, if any,
    	 * or otherwise as a static method on the local bean class.
    	 * @see #setFactoryBeanName
    	 * @see #setBeanClassName
    	 */
    	void setFactoryMethodName(@Nullable String factoryMethodName);
    
    	/**
    	 * Return a factory method, if any.
    	 */
    	@Nullable
    	String getFactoryMethodName();

*  getConstructorArgumentValues() 和 getPropertyValues()：获取构造函数参数值和属性值。

/**
 	 * Return the constructor argument values for this bean.
 	 * The returned instance can be modified during bean factory post-processing.
 	 * @return the ConstructorArgumentValues object (never {@code null})
 	 */
 	ConstructorArgumentValues getConstructorArgumentValues();
 
 
 **
 	 * Return the property values to be applied to a new instance of the bean.
 	 * The returned instance can be modified during bean factory post-processing.
 	 * @return the MutablePropertyValues object (never {@code null})
 	 */
 	MutablePropertyValues getPropertyValues();

*  setInitMethodName(String initMethodName) 和 getInitMethodName()：设置和获取初始化方法的名称。

/**
    	 * Set the name of the initializer method.
    	 * @since 5.1
    	 */
    	void setInitMethodName(@Nullable String initMethodName);
    
    	/**
    	 * Return the name of the initializer method.
    	 * @since 5.1
    	 */
    	@Nullable
    	String getInitMethodName();

*  setDestroyMethodName(String destroyMethodName) 和 getDestroyMethodName()：设置和获取销毁方法的名称。

/**
    	 * Set the name of the destroy method.
    	 * @since 5.1
    	 */
    	void setDestroyMethodName(@Nullable String destroyMethodName);
    
    	/**
    	 * Return the name of the destroy method.
    	 * @since 5.1
    	 */
    	@Nullable
    	String getDestroyMethodName();

*  setRole(int role) 和 getRole()：设置和获取 Bean 的角色。

/**
    	 * Set the role hint for this {@code BeanDefinition}. The role hint
    	 * provides the frameworks as well as tools an indication of
    	 * the role and importance of a particular {@code BeanDefinition}.
    	 * @since 5.1
    	 * @see #ROLE_APPLICATION
    	 * @see #ROLE_SUPPORT
    	 * @see #ROLE_INFRASTRUCTURE
    	 */
    	void setRole(int role);
    
    	/**
    	 * Get the role hint for this {@code BeanDefinition}. The role hint
    	 * provides the frameworks as well as tools an indication of
    	 * the role and importance of a particular {@code BeanDefinition}.
    	 * @see #ROLE_APPLICATION
    	 * @see #ROLE_SUPPORT
    	 * @see #ROLE_INFRASTRUCTURE
    	 */
    	int getRole();

*  setDescription(String description) 和 getDescription()：设置和获取 Bean 的描述信息。

/**
    	 * Set a human-readable description of this bean definition.
    	 * @since 5.1
    	 */
    	void setDescription(@Nullable String description);
    
    	/**
    	 * Return a human-readable description of this bean definition.
    	 */
    	@Nullable
    	String getDescription();

*  getResolvableType()：获取 Bean 的可解析类型。

/**
 	 * Return a resolvable type for this bean definition,
 	 * based on the bean class or other specific metadata.
 	 * This is typically fully resolved on a runtime-merged bean definition
 	 * but not necessarily on a configuration-time definition instance.
 	 * @return the resolvable type (potentially {@link ResolvableType#NONE})
 	 * @since 5.2
 	 * @see ConfigurableBeanFactory#getMergedBeanDefinition
 	 */
 	ResolvableType getResolvableType();

*  isSingleton() 和 isPrototype()：判断 Bean 是否为单例和原型。

/**
 	 * Return whether this a Singleton, with a single, shared instance
 	 * returned on all calls.
 	 * @see #SCOPE_SINGLETON
 	 */
 	boolean isSingleton();
 
 	/**
 	 * Return whether this a Prototype, with an independent instance
 	 * returned for each call.
 	 * @since 3.0
 	 * @see #SCOPE_PROTOTYPE
 	 */
 	boolean isPrototype();

*  isAbstract()：判断 Bean 是否为抽象 Bean。

/**
    	 * Return whether this bean is "abstract", that is, not meant to be instantiated.
    	 */
    	boolean isAbstract();

*  getResourceDescription()：获取 Bean 定义的资源描述。

/**
    	 * Return a description of the resource that this bean definition
    	 * came from (for the purpose of showing context in case of errors).
    	 */
    	@Nullable
    	String getResourceDescription();

*  getOriginatingBeanDefinition()：获取 Bean 定义的来源 Bean 定义，如果有的话。

/**
 	 * Return the originating BeanDefinition, or {@code null} if none.
 	 * Allows for retrieving the decorated bean definition, if any.
 	 * Note that this method returns the immediate originator. Iterate through the
 	 * originator chain to find the original BeanDefinition as defined by the user.
 	 */
 	@Nullable
 	BeanDefinition getOriginatingBeanDefinition();

通过 BeanDefinition 接口提供的各种方法，Spring 容器可以了解到 Bean 的各种属性信息，并据此进行实例化、依赖注入、生命周期管理等操作。